Guide wire

ABSTRACT

A guide wire includes a first wire disposed on the distal side, and a second wire disposed on the proximal side and made from a material having an elastic modulus larger than that of the first wire. The first wire and the second wire are joined to each other by welding. The second wire has, in the vicinity of the welded portion, a small cross-sectional area portion having a cross-sectional area smaller than that of a proximal end portion of the first wire. The outer diameter of the small cross-sectional area portion is gradually reduced in the direction toward the distal end. The first wire and the second wire may be welded to each other by a butt resistance welding process. Since the change in rigidity of the guide wire becomes smooth in the longitudinal direction, the operationality and kink resistance of the guide wire are improved.

This application is a continuation of prior application Ser. No.11/797,328 filed on May 2, 2017, which is a divisional of priorapplication Ser. No. 10/635,716 filed on Aug. 7, 2003, which claims thebenefit of Japanese Patent Application No. 2002-232164 filed on Aug. 8,2002, Japanese Patent Application No. 2002-355908 filed on Dec. 6, 2002and Japanese Patent Application No. 2003-156011 filed on May 30, 2003.The entire content of the prior applications is hereby incorporated byreference here in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a guide wire, particularly to a guidewire used to guide a catheter in a body lumen such as a blood vessel.

2. Description of the Related Art

Guide wires are used to guide a catheter in treatment of cites at whichopen surgeries are difficult or which require minimally invasiveness tothe body, for example, PTCA (Percutaneous Transluminal CoronaryAngioplasty), or in examination such as cardio-angiography. A guide wireused in the PTCA procedure is inserted, with the distal end projectingfrom the distal end of a balloon catheter, into the vicinity of a targetangiostenosis portion together with the balloon catheter, and isoperated to guide the distal end portion of the balloon catheter to thetarget angiostenosis portion.

A guide wire used to insert a catheter into a blood vessel complicatedlybent requires appropriate flexibility and restoring performance againstbending, pushability and torque transmission performance (genericallycalled “operationality”) for transmitting an operational force from theproximal end portion to the distal side, and kink resistance (oftencalled “resistance against sharp bending”). To obtain appropriateflexibility as one of the above-described performances, there has beenknown a guide wire configured such that a metal coil having flexibilityis provided around a small-sized core member at the distal end of theguide wire, or a guide wire including a core member made from asuperelastic material such as an Ni—Ti alloy for improving theflexibility and restoring performance.

Conventional guide wires include a core member that is substantiallymade from a single material. In particular, to enhance theoperationality of the guide wire, a material having a relatively highelastic modulus is used as the material of the core member. The guidewire including such a core member, however, has an inconvenience thatthe distal end portion of the guide wire becomes lower in flexibility.On the other hand, if a material having a relatively low elastic modulusis used as the material of the core member for increasing theflexibility of the distal end portion of the guide wire, theoperationality of the proximal end portion of the guide wire isdegraded. In this way, it has been regarded as difficult to satisfy bothrequirements associated with the flexibility and operationality by usinga core member made from a single material.

A guide wire intended to solve such a problem has been disclosed, forexample, in U.S. Pat. No. 5,171,383, wherein a Ni—Ti alloy wire is usedas a core member, and the distal side and the proximal side of the alloywire are heat-treated under different conditions in order to enhance theflexibility of the distal end portion of the alloy wire while enhancingthe rigidity of the proximal side of the alloy wire. Such a guide wire,however, has a problem that the control of the flexibility of the distalend portion by heat-treatment has a limitation. For example, even if itis successful to obtain a sufficient flexibility of the distal endportion of the alloy wire, it may often fail to obtain a sufficientrigidity on the proximal side of the alloy wire.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a guide wire capable ofmaking the change in rigidity smooth in the longitudinal direction ofthe guide wire, thereby improving the operationality and kink resistanceof the guide wire.

To achieve the above object, according to a first aspect of the presentinvention, there is provided a guide wire including a first wiredisposed on the distal side of the guide wire, and a second wiredisposed on the proximal side from the first wire, the second wire beingmade from a material having an elastic modulus larger than that of thefirst wire, wherein the first wire and second wire are joined to eachother by welding, and the second wire has, in the vicinity of a weldedportion between the first wire and the second wire, a smallcross-sectional area portion having a cross-sectional area smaller thana cross-sectional area of a proximal end portion of the first wire.

According to a second aspect of the present invention, there is provideda guide wire including a first wire disposed on the distal side of theguide wire, and a second wire disposed on the proximal side from thefirst wire, the second wire having a rigidity higher than a rigidity ofthe first wire, wherein the first wire and the second wire are joined toeach other by welding, and a welded portion formed by welding has aprojection projecting in the outer peripheral direction, and the secondwire has, in the vicinity of a welded portion between the first wire andthe second wire, a small cross-sectional area portion having across-sectional area smaller than a cross-sectional area of a proximalend portion of the first wire.

Each of the guide wires according to the first and second aspects of thepresent invention may be further configured as follows.

The guide wire preferably includes a cover layer disposed over at leastthe welded portion.

The small cross-sectional area portion preferably has an outer diametersmaller than an outer diameter of the proximal end portion of the firstwire.

The small cross-sectional area portion preferably includes a portionhaving a cross-sectional area gradually reduced in the direction towardthe distal end of the guide wire.

The small cross-sectional area portion preferably includes a portionhaving an outer-diameter gradually reduced in the direction toward thedistal end of the guide wire.

The small cross-sectional area portion preferably includes a firstportion having an outer diameter gradually reduced in the directiontoward the distal end of the guide wire, and a second portion having anouter diameter gradually increased in the direction toward the distalend of the guide wire, the second portion being disposed on the distalside from the first portion.

The small cross-sectional area portion preferably has a third portionhaving a nearly constant outer diameter, the third portion beingdisposed between the first portion and the second portion.

The first portion preferably has a length in a range of 0.1 to 1,000times a length of the second portion.

A flexural rigidity of the distal end of the second wire is preferablynearly equal to a flexural rigidity of the proximal end of the firstwire.

The guide wire preferably further includes a step filling member forfilling a stepped portion formed on the outer periphery of the weldedportion.

An outer peripheral surface of a boundary portion between the firstportion and the second portion may form a continuous curved planewithout any stepped portion.

Each of an outer peripheral surface of a boundary portion between thefirst portion and the third portion and an outer peripheral surface of aboundary portion between the third portion and the second portion mayform a continuous curved plane without any stepped portion.

The first wire may be made from a superelastic alloy.

The second wire may be made from a stainless steel.

The second wire may be made from a Co-based alloy.

The Co-based alloy may be a Co—Ni—Cr alloy.

Each of a connection end face of the first wire to the second wire and aconnection end face of the second wire to the first wire may be nearlyperpendicular to the axial direction of the first and second wires.

The guide wire may further include a spiral coil covering at least adistal end portion of the first wire.

The welded portion may be located on the proximal side from the proximalend of the coil.

The first wire and the second wire may be welded to each other by a buttresistance welding process.

The guide wire may be used in such a manner that the welded portion belocated in a living body.

As described above, since the guide wire of the present invention hasthe first wire disposed on the distal side and the second wire disposedon the proximal side from the first wire and made from a material havingan elastic modulus larger than that of the first wire, it is possible toensure a high rigidity at a proximal end portion while keeping a highflexibility at a distal end portion, and hence to enhance thepushability, torque transmission performance, and trackability of theguide wire.

Since the first wire and the second wire are joined to each other bywelding, it is possible to enhance the joining strength of the joiningportion (welded portion), and hence to certainly transmit a torsionaltorque or pushing force from the second wire to the first wire.

Since the small cross-sectional area portion is provided on the secondwire, it is possible to make the change in rigidity of the weldedportion and its neighborhood smooth in the longitudinal direction, andhence to certainly prevent kink (sharp bending) or torsion of a portionin the vicinity of the welded portion.

Since the shape of the small cross-sectional area portion is contrived,for example, in such a manner that the small cross-sectional areaportion is divided into two parts (first and second portions) or threeparts (first, second, and third portions), it is possible to enhance thewelding strength of the welded portion, and to relieve or disconcentratelocal stress concentration at the small cross-sectional area portion andhence to more certainly prevent kink and torsion.

Accordingly, the present invention can provide a guide wire excellent inoperationality, kink resistance, and torsion resistance.

With the configuration that the projection is formed on the weldedportion, it is possible to further enhance the joining strength of thejoining portion (welded portion) and hence to more certainly transmit atorsional torque or pushing force from the second wire to the firstwire.

With the configuration that the cover layer is made from a materialcapable of reducing the friction of the cover layer, it is possible toimprove the sliding resistance of the guide wire in a catheter and henceto further enhance the operationality of the guide wire. Since thesliding resistance of the guide wire is reduced, it is possible to morecertainly prevent kink (sharp bending) and torsion of the guide wire,particularly, in the vicinity of the welded portion.

By changing materials used for the cover layer at respective portions,it is possible to enhance the sliding resistance at each of the portionsand hence to expand the versability for an operator.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription in conjunction with the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view showing a first embodiment of aguide wire of the present invention;

FIGS. 2A to 2C are views showing steps of a procedure for connecting afirst wire and a second wire of the guide wire shown in FIG. 1;

FIG. 3 is a typical view illustrating an example of how to use the guidewire of the present invention;

FIG. 4 is a typical view illustrating the example of how to use theguide wire of the present invention;

FIG. 5 is a longitudinal sectional view showing a modification of asmall cross-sectional area portion of the guide wire of the presentinvention;

FIG. 6 is a longitudinal sectional view showing another modification ofa small cross-sectional area portion of the guide wire of the presentinvention;

FIG. 7 is a longitudinal sectional view showing a second embodiment ofthe guide wire of the present invention; and

FIGS. 8A and 8B are perspective views showing further modifications ofthe small cross-sectional area portion of a second wire of the guidewire of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A guide wire of the present invention will now be described in detail byway of preferred embodiments shown in the accompanying drawings.

FIG. 1 is a longitudinal sectional view of a first embodiment of a guidewire of the present invention, and FIGS. 2A to 2C are views showing aprocedure for joining a first wire and a second wire of the guide wireshown in FIG. 1 to each other. For convenience of description, the rightside in FIG. 1 is taken as the “proximal side” and the left side in FIG.1 is taken as the “distal side”. It is to be noted that in FIG. 1 (andin FIGS. 5 to 7 to be described later), for easy understanding, thedimension of the guide wire in the thickness direction is exaggeratedlyenlarged while the dimension of the guide wire in the length directionis shortened, and therefore, the ratio of the thickness to the length issignificantly different from the actual ratio.

A guide wire 1 shown in FIG. 1, which is of a type used to be insertedin a catheter, includes a first wire 2 disposed on the distal side, asecond wire 3 disposed on the proximal side from the first wire 2, and aspiral coil 4. The entire length of the guide wire 1 is not particularlylimited but is preferably in a range of about 200 to 5,000 mm. The outerdiameter of the guide wire 1 is not particularly limited but ispreferably in a range of about 0.2 to 1.2 mm.

The first wire 2 is configured as a wire member having elasticity. Thelength of the first wire 2 is not particularly limited but is preferablyin a range of about 20 to 1,000 mm.

According to this embodiment, the first wire 2 has, at its distal endportion, an outer-diameter gradually reducing portion 22 with its outerdiameter gradually reduced in the direction toward the distal end. Inthe outer-diameter gradually reducing portion 22 of the first wire 2,therefore, the rigidity (flexural rigidity, torsional rigidity) isgradually reduced in the direction toward the distal end. As a result,it is possible to enhance the flexibility of the distal end portion ofthe guide wire 1, and hence to improve the follow-up performance andsafety to a blood vessel and also to prevent sharp-bending and the like.

In the configuration shown in the figure, the first wire 2 has, nearlyover the entire length, a taper shape in which the outer diameter iscontinuously, gradually reduced in the direction toward the distal end.The taper angle of the taper portion of the first wire 2 may be keptconstant or changed along the longitudinal direction.

According to this embodiment, the outer-diameter gradually reducingportion 22 is tapered such that the outer diameter is continuouslyreduced with a nearly constant reduction ratio in the direction towardthe distal end. In other words, the taper angle of the outer-diametergradually reducing portion 22 is kept nearly constant along thelongitudinal direction. In the outer-diameter gradually reducing portion22, therefore, the change in rigidity becomes more moderate (or smooth)along the longitudinal direction. Unlike such a configuration, thereduction ratio of the outer diameter of the outer-diameter graduallyreducing portion 22 (taper angle of the outer-diameter graduallyreducing portion 22) may be changed along the longitudinal direction.For example, portions in each of which the reduction ratio of the outerdiameter is relatively large and portions in each of which the reductionratio of the outer diameter is relatively small may be alternatelyrepeated by a plurality of numbers. In this case, the outer-diametergradually reducing portion 22 may have a portion in which the reductionratio of the outer diameter in the direction toward the distal endbecomes zero.

The outer diameter of a proximal end portion of the first wire 2 is keptnearly constant along the longitudinal direction. Unlike theconfiguration shown in the figure, the outer diameter of nearly thewhole of the first wire 2 may be gradually reduced in the directiontoward the distal end. In other words, nearly the whole of the firstwire 2 may be composed of the outer-diameter gradually portion 22.

The material for forming the first wire 2 is not particularly limitedbut may be selected from metal materials such as stainless steels. Inparticular, alloys having pseudo-elasticity (for example, superelasticalloys) are preferable, and superelastic alloys are more preferable.Superelastic alloys are relatively flexible, good in restoringperformance, and less susceptible to reforming. Accordingly, if thefirst wire 2 is made from a superelastic alloy, the guide wire 1including such a first wire 2 has, at its distal portion, a highflexibility and a high restoring performance against bending, and a hightrackability to a blood vessel complicatedly curved or bent, to therebyenhance the operationality of the guide wire 1. Even if the first wire 2is repeatedly deformed, that is, curved or bent, the first wire 2 is noor less plastic deforming because of its high restoring performance.This prevents degradation of the operationality due to the plasticdeforming of the first wire 2 during use of the guide wire 1.

Pseudo-elastic alloys include those of a type in which the stress-straincurve in a tensile test has any shape, those of a type in which atransformation point such as As, Af, Ms, or Mf can be significantlymeasured or not measured, and those of all types in which the shape isgreatly deformed by stress and then restored nearly to an original shapeby removal of stress.

Examples of superelastic alloys include Ni—Ti alloys such as an Ni—Tialloy containing Ni in an amount of 49-52 atomic %, a Cu—Zn alloycontaining Zn in an amount of 38.5 to 41.5 wt %, a Cu—Zn—X alloycontaining X in an amount of 1 to 10 wt % (X: at least one kind selectedfrom a group consisting of Be, Si, Sn, Al, and Ga), and an Ni—Al alloycontaining Al in an amount of 36 to 38 atomic %. Of these materials, theNi—Ti alloy is preferable.

The distal end of the second wire 3 is joined to the proximal end of thefirst wire 2. The second wire 3 is a wire member having elasticity. Thelength of the second wire 3 is not particularly limited but may be in arange of about 20 to 4,800 mm.

The second wire 3 is made from a material having an elastic modulus(Young's modulus or modulus of longitudinal elasticity, modulus ofrigidity or modulus of transverse elasticity, or bulk modulus) largerthan that of the first wire 2. The second wire 3 can thus exhibit anappropriate rigidity (flexural rigidity, torsional rigidity). As aresult, the guide wire 1 becomes firm, to improve the pushability andtorque transmission performance, thereby enhancing the operationality atthe time of insertion of the guide wire 1.

The material for forming the second wire 3 is not particularly limitedbut may be selected from metal materials, for example, stainless steels(all kinds specified in SUS, for example, SUS304, SUS303, SUS316,SUS316L, SUS316J1, SUS316J1L, SUS405, SUS430, SUS434, SUS444, SUS429,SUS430F, and SUS302), piano wire steels, cobalt alloys, and alloyshaving pseudo-elasticity.

In particular, cobalt alloys are preferably used for the second wire 3.This is because the second wire 3 made from a cobalt alloy has a highelastic modulus and an appropriate elastic limit. Such a second wire 3exhibits a good torque transmission performance, thereby hardly causinga problem associated with buckling or the like. Any type of cobalt alloymay be used insofar as it contains cobalt. In particular, a cobalt alloycontaining cobalt as a main component (that is, a cobalt-based alloycontaining cobalt in an amount [in wt %] being the largest among thecontents of all components of the alloy) is preferably used, andfurther, a Co—Ni—Cr alloy is more preferable. The use of the cobaltalloy having such a composition as the material for forming the secondwire 3 is effective to further enhance the above-described effects. Thecobalt alloy having such a composition is also advantageous in thatsince the alloy exhibits plasticity in deformation at room temperature,the second wire 3 made from such a cobalt alloy is easily deformableinto a desired shape, for example, during use of the guide wire. Afurther advantage of the cobalt alloy having such a composition is asfollows: namely, since the second wire 3 made from such a cobalt alloyhas a high elastic modulus and is cold-formable even if it exhibits ahigh elastic limit, the second wire 3 can be thinned while sufficientlypreventing occurrence of buckling, and therefore, can exhibit a highflexibility and a high rigidity enough to be inserted into a desiredsite.

The Co—Ni—Cr alloy is exemplified by an alloy containing 28-50 wt % ofCo, 10-30 wt % of Ni, and 10-30 wt % of Cr, the balance being Fe. Inthis alloy, part of any component may be substituted by another element(substitution element). The incorporation of such a substitution elementexhibits an effect inherent to the kind thereof. For example, theincorporation of at least one kind selected from a group consisting ofTi, Nb, Ta, Be, and Mo further improves the strength of the second wire3. In the case of incorporating one or more substitution elements otherthan Co, Ni, and Cr, the total content of the substitution elements ispreferably in a range of 30 wt % or less.

For example, part of Ni may be substituted by Mn, which is effective tofurther improve the workability. Part of Cr may be substituted by Moand/or W, which is effective to further improve the elastic limit. Ofthe Co—Ni—Cr alloys, a Co—Ni—Cr—Mo alloy is particularly preferable.

Examples of compositions of the Co—Ni—Cr alloys include (1) 40 wt %Co-22 wt % Ni-25 wt % Cr-2 wt % Mn-0.17 wt % C-0.03 wt % Be—Fe(balance),(2) 40 wt % Co-15 wt % Ni-20 wt % Cr-2 wt % Mn-7 wt % Mo-0.15 wt %C-0.03 wt % Be—Fe(balance), (3) 42 wt % Co-13 wt % Ni-20 wt % Cr-1.6 wt% Mn-2 wt % Mo-2.8 wt % W-0.2 wt % C-0.04 wt % Be—Fe(balance), (4) 45 wt% Co-21 wt % Ni-18 wt % Cr-1 wt % Mn-4 wt % Mo-1 wt % Ti-0.02 wt % C-0.3wt % Be—Fe(balance), and (5) 34 wt % Co-21 wt % Ni-14 wt % Cr-0.5 wt %Mn-6 wt % Mo-2.5 wt % Nb-0.5 wt % Ta—Fe(balance). The wording “Co—Ni—Cralloy” used herein is the conception including these Co—Ni—Cr alloys.

If a stainless steel is used as the material for forming the second wire3, the pushability and torque transmission performance of the guide wire1 can be further enhanced.

The first wire 2 and the second wire 3 may be made from differentalloys, and particularly, the first wire 2 is preferably made from amaterial having an elastic modulus smaller than that of the material ofthe second wire 3. With this configuration, the distal end portion ofthe guide wire 1 has a high flexibility, and the proximal end portion ofthe guide wire 1 has a high rigidity (flexural rigidity, torsionalrigidity). As a result, the guide wire 1 has a high pushability and ahigh torque transmission performance, thereby enhancing theoperationality, and also exhibits, on the distal side, a highflexibility and a high restoring performance, thereby improvingtrackability and safety to a blood vessel.

As one preferred combination of materials of the first wire 2 and thesecond wire 3, the first wire 2 is made from a superelastic alloy andthe second wire 3 is made from a Co—Ni—Cr alloy or a stainless steel.With this configuration, the above-described effects become moresignificant.

From the viewpoint of enhancing the flexibility and restoringperformance of the distal end portion of the first wire 2, it ispreferred to use a Ni—Ti alloy as the superelastic alloy for forming thefirst wire 2.

The coil 4 is a member formed by spirally winding a wire, particularly afine wire, and is provided so as to cover the distal end portion of thefirst wire 2. In the configuration shown in FIG. 1, the distal endportion of the first wire 2 is disposed in an approximately axiallycenter portion of the coil 4 in such a manner as to be not in contactwith the inner surface of the coil 4. It is to be noted that in theconfiguration shown in FIG. 1, the coil 4 is loosely disposed in such amanner that a slight gap remains between adjacent spirally wound wireportions in a state that no external force is applied to the coil 4;however, the coil 4 may be tightly disposed in such a manner that no gapremains between the adjacent spirally wound wire portions in a statethat no external force is applied to the coil 4.

The coil 4 may be made from a metal material such as a stainless steel,a superelastic alloy, a cobalt alloy, a noble metal such as gold,platinum, or tungsten, or an alloy containing such a noble metal. Inparticular, the coil 4 is preferably made from a radiopaque materialsuch as a noble metal. If the coil 4 is made from such a radiopaquematerial, the guide wire 1 can exhibit an X-ray contrast performance.This makes it possible to insert the guide wire 1 in a living body whileconfirming the position of the distal end portion of the guide wire 1under fluoroscopy. The distal side and proximal side of the coil 4 maybe made from different alloys. For example, the distal side of the coil4 may be formed of a coil made from a radiopaque material and theproximal side of the coil 4 be formed of a coil made from a relativelyradiolucent material such as a stainless material. The entire length ofthe coil 4 is not particularly limited but may be in a range of about 5to 500 mm.

The proximal end portion and the distal end portion of the coil 4 arefixed to the first wire 2 by a fixing material 11 and a fixing material12, respectively, and an intermediate portion (close to the distal end)of the coil 4 is fixed to the first wire 2 by a fixing material 13. Eachof the fixing materials 11, 12, and 13 is a solder (brazing material).Alternatively, each of the fixing materials 11, 12, and 13 may be anadhesive. In addition, in place of using the fixing material, the coil 4may be fixed to the first wire 2 by welding. To prevent damage of theinner wall of a blood vessel, the leading end surface of the fixingmaterial 12 is preferably rounded.

According to this embodiment, since the first wire 2 is partiallycovered with the coil 4, the contact area of the first wire 2 with theinner wall of a catheter used together with the guide wire 1 is small,with a result that it is possible to reduce the sliding resistance ofthe guide wire 1 in the catheter. This is effective to further improvethe operationality of the guide wire 1.

In this embodiment, the wire having a circular shape in cross-section isused for the coil 4; however, the cross-sectional shape of the wire usedfor the coil 4 may be another shape such as an elliptic shape or aquadrilateral shape (especially, rectangular shape).

In the guide wire 1, the first wire 2 and the second wire 2 are joinedto each other by welding. A welded portion (joining portion) 14 betweenthe first wire 2 and the second wire 3 has a high joining strength,thereby allowing the guide wire 1 to certainly transmit a torsionaltorque or pushing force from the second wire 3 to the first wire 2.

In this embodiment, a connection end face 21 of the first wire 2 to thesecond wire 3 and a connection end face 31 of the second wire 3 to thefirst wire 2 are each formed into a plane nearly perpendicular to theaxial (longitudinal) direction of both the wires 2 and 3. Thissignificantly facilitates working for forming the connection end faces21 and 31, to achieve the above-described effects without complicatingthe steps for producing the guide wire 1.

It is to be noted that each of the connection end faces 21 and 31 may betilted relative to the plane perpendicular to the axial (longitudinal)direction of both the wires 2 and 3, or formed into a recessed or raisedshape.

The method of welding the first wire 2 and the second wire 3 to eachother is not particularly limited but is generally exemplified by spotwelding using laser or butt resistance welding such as butt seamwelding. In particular, to ensure a high joining strength of the weldedportion, butt resistance welding is preferable.

The second wire 3 of the guide wire 1 has, in the vicinity of the weldedportion 14, a small cross-sectional area 32 with its cross-sectionalarea being smaller than that of a proximal end portion 23 of the firstwire 2. In other words, in a portion from the connection end face 31 toa specific position on the proximal side, that is, in the smallcross-sectional area portion 32, the cross-sectional area of the secondwire 3 is smaller than that of the proximal end portion 23 of the firstwire 2. In this embodiment, the outer diameter of the smallcross-sectional area portion 32 is smaller than that of the proximal endportion 23 of the first wire 2, and therefore, the cross-sectional areaof the small cross-sectional area portion 32 is smaller than that of theproximal end portion 23. In other words, the area of the connection endface 31 is smaller than that of the connection end face 21.

Since the second wire 3 is made from a material having an elasticmodulus larger than that of the first wire 2 as described above, if theouter diameter of the distal end portion of the second wire 3 is thesame as that of the proximal end portion 23 of the first wire 2, therigidity (flexural rigidity, torsional rigidity) of the guide wire 1 israpidly changed between both sides of the welded portion 14. On thecontrary, according to the present invention, the small cross-sectionalarea portion 32 is provided at the distal end portion of the second wire3, and the rigidity (flexural rigidity, torsional rigidity) of the smallcross-sectional area portion 32 is made small. Accordingly, the changein rigidity (flexural rigidity, torsional rigidity) of the weldedportion 14 and its neighborhood becomes moderate (smooth) along thelongitudinal direction, to thereby enhance the operationality of theguide wire 1.

According to this embodiment, the small cross-sectional area portion 32includes a portion in which the outer diameter is gradually reduced inthe direction toward the distal end, that is, the cross-sectional areais gradually reduced in the direction toward the distal end.Accordingly, the rigidity (flexural rigidity, torsional rigidity) of thesmall cross-sectional area portion 32 is gradually reduced from theproximal end to the distal end thereof, that is, in the direction towardthe distal end of the guide wire 1, to thereby make the change inrigidity (flexural rigidity, torsional rigidity) of the guide wire 1more moderate (smooth) along the longitudinal direction.

In the configuration shown in the figure, the small cross-sectional areaportion 32 has, over the entire length, the taper shape with its outerdiameter gradually reduced in the direction toward the distal end;however, the small cross-sectional area portion 32 may have a portionhaving a constant outer diameter (cross-sectional area), for example, onthe distal end side, and may further have, on the distal side from theouter-diameter constant portion, a portion with its outer diametergradually increased in the direction toward the welded portion 14. Evenin this case, the same effect as that described above can be obtained.It is to be noted that modifications of the small cross-sectional areaportion 32 will be fully described in detail.

The length of the small cross-sectional area portion 32 (denoted bycharacter L in FIG. 1) is not particularly limited but is preferably ina range of about 3 to 1,000 mm, more preferably, about 3 to 300 mm. Ifthe length L is within the above range, the change in rigidity (flexuralrigidity, torsional rigidity) of the welded portion 14 and itsneighborhood can be made more moderate (smooth) along the longitudinaldirection.

In the small cross-sectional area portion 32, the flexural rigidity ofthe distal end (connection end face 31) of the second wire 3 ispreferably nearly equal to the flexural rigidity of the proximal end(connection end face 21) of the first wire 2. With this configuration,the change in rigidity of the welded portion 14 and its neighborhood canbe made more moderate (smooth) along the longitudinal direction. Inaddition, letting the geometrical moment of inertia (determined only bythe shape and dimension of the connection end face 31) of the connectionend face 31 be I₂ and the Young's modulus of the material of the secondwire 3 be E₂, the flexural rigidity of the distal end of the second wire3 is expressed by E₂·I₂. On the other hand, letting the geometricalmoment of inertia (determined only by the shape and dimension of theconnection end face 21) of the connection end face 21 be I₁ and theYoung's modulus of the material of the first wire 2 be E₁, the flexuralrigidity of the distal end of the first wire 2 is expressed by E₁·I₁.

The guide wire 1 in this embodiment has a step filling member 6 forfilling a stepped portion formed on the outer periphery of the weldedportion 14. The stepped portion, which is formed on the outer peripheryof the welded portion 14 due to the fact that the outer diameter of thedistal end of the second wire 3 is smaller than that of the proximal endof the first wire 2, is filled with the step filling member 6, tothereby prevent the reduction in sliding performance of the guide wire 1due to the presence of the stepped portion.

In the configuration shown in the figure, the step filling member 6covers the small cross-sectional area portion 32. The outer diameter ofthe member 6 is kept nearly constant along the longitudinal direction,and the inner diameter of the member 6 is gradually reduced in thedirection toward the distal end. As a result, the outer diameter of aportion, including the welded portion 14 and the small cross-sectionalarea portion 32, of the guide wire 1 is kept nearly constant along thelongitudinal direction. This is effective to more certainly eliminateadverse effect of the stepped portion exerted on the sliding performanceof the guide wire 1.

The material for forming the step filling member 6 is not particularlylimited, and may be generally selected from resin materials and metalmaterials. To reduce adverse effect of the member 6 exerted on therigidity of the guide wire 1, the member 6 is preferably made from arelative soft material such as solder, plastic, or wax. The shape of thestep filling member 6 is not limited to that shown in the figure but maybe any shape such as a coil shape.

In this embodiment, the welded portion 14 is located on the proximalside from the proximal end of the coil 4, but the welded portion 14 maybe located on the distal side from the proximal end of the coil 4.

If the rigidity of the first wire 2 is smaller than that of the secondwire 3, the size of the connection end face 31 may be larger than thatof the connection end face 21.

FIGS. 5 and 6 are longitudinal sectional views showing modifications ofthe small cross-sectional area portion of the guide wire of the presentinvention.

A small cross-sectional area portion 32 according to a modificationshown in FIG. 5 has a first portion 32A with its outer diametergradually reduced in the direction toward the distal end, and a secondportion 32B with its outer diameter gradually increased in the directiontoward the distal end, wherein the second portion 32B is disposed on thedistal side from the first portion 32A. The outer peripheral surface ofa boundary portion between the first portion 32A and the second portion32B has a continuous curved plane without substantial stepped portion(smooth plane). With this configuration, it is possible to prevent orrelieve stress concentration at the boundary portion, and hence to morecertainly prevent torsion or kink, that is, to improve the kinkresistance.

The maximum outer diameter of the second portion 32B is located at aconnection end face 31 (the distal end of a second wire 3), and isnearly equal to the outer diameter of a connection end face 21 (theproximal end of a first wire 2). Accordingly, as compared with theconfiguration shown in FIG. 1, the small cross-sectional area portion 32shown in FIG. 5 is advantageous in enlarging the area of a weldedsurface of a welded portion 14, thereby improving the welding strength.As a result, when a torsional torque or pushing force is applied fromthe second wire 3 to the first wire 2, it is possible to more certainlyprevent breakage of the welded portion 14 due to stress concentration atthe welded portion 14 or lacking of the welding strength of the weldedportion 14.

In the small cross-sectional area portion 32, letting the length of thefirst portion 32A be L_(A) and the length of the second portion 32B beL_(B), the length L_(A) is longer than the length L_(B). In other words,the taper angle of the first portion 32A is smaller than that of thesecond portion 32B.

The length L_(A) of the first portion 32A is preferably in a range ofabout 0.1 to 1,000 times, more preferably, 1.0 to 1,000 times, mostpreferably, 1.0 to 50 times the length L_(B) of the second portion 32B.With this configuration, it is possible to suppress stress concentrationat the welded portion 14, and hence to realize smooth transition ofrigidity.

A small cross-sectional area portion 32 according to anothermodification shown in FIG. 6 has a third portion 32C located between afirst portion 32A and a second portion 32B. The third portion 32C has anearly constant outer diameter, which may be smaller than each of theouter diameters of the first portion 32A and the second portion 32B. Inother words, the third portion 32C is preferably the minimumouter-diameter portion of the small cross-sectional area portion 32.Other configurations of this modification are the same as those of theprevious modification shown in FIG. 5.

The small cross-sectional area portion 32 shown in FIG. 6 has not onlythe same function and effect as those of the small cross-sectional areaportion 32 shown in FIG. 5, but also the following additional functionand effect: namely, since the minimum outer-diameter portion of thesmall cross-sectional area portion 32 may be taken as the third portion32C continuously extending for a specific length (denoted by characterL_(c)), it is possible to more certainly relieve stress concentration atthe minimum outer-diameter portion of the small cross-sectional portion32 as compared with the configuration shown in FIG. 5. As a result, whena torsional torque or pushing force is applied from the second wire 3 tothe first wire 2, it is possible to more certainly prevent torsion,kink, breakage, and the like of the minimum outer-diameter portion ofthe small cross-sectional area portion 32.

The third portion 32C preferably has rigidity nearly equal to that of aportion in the vicinity of the proximal end portion 23 of the first wire2. Since the outer diameter of the third portion 32C is set such thatthe rigidity of the third portion 32C is nearly equal to the portion inthe vicinity of the proximal end portion 23 of the first wire 2, it ispossible to realize smooth transition of rigidity from the smallcross-sectional area portion 32 to the proximal end portion 23 of thefirst wire 2.

Each of the outer peripheral surface of a boundary portion between thefirst portion 32A and the third portion 32C and the outer peripheralsurface of a boundary portion between the third portion 32C and thesecond portion 32B forms a continuously curved plane without substantialstepped portion (smooth plane). With this configuration, theabove-described effect of preventing or relieving stress concentrationat the boundary portion can be obtained.

The relationship among a length L_(A) of the first portion 32A, a lengthL_(B) of the second portion 32B, and a length L_(C) of the third portion32C is not particularly limited but is preferably set to a relationshipof L_(B)≦L_(C)≦L_(A) or L_(B)≦L_(A)≦L_(C), more preferablyL_(B)<L_(C)≦L_(A).

In this embodiment, the length L_(A) of the first portion 32A ispreferably in a range of about 0.1 to 1,000 times, more preferably, 0.1to 10 times the length L_(B) of the second portion 32B. With thisconfiguration, it is possible to suppress stress concentration at thewelded portion 14, and hence to realize smooth transition of rigidity.

To sufficiently obtain an effect of relieving stress concentration atthe minimum outer-diameter portion while keeping the strength of thesmall cross-sectional area portion 32, the length L_(C) of the thirdportion 32C is preferably in a range of about 0.1 to 200 mm, morepreferably, about 1 to 50 mm.

The outer periphery of the small cross-sectional area portion 32 shownin each of FIGS. 5 and 6 may be covered with the above-described stepfilling member 6. With this configuration, the above-described effect ofeliminating the degradation of the sliding performance of the guide wire1 due to the presence of the stepped portion can be obtained.

The procedure of joining the first wire 2 and the second wire 3 to eachother by butt seam welding as one example of butt resistance weldingwill be described with reference to FIGS. 2A to 2C. FIGS. 2A to 2C showsteps 1 to 3 of the procedure of joining the first wire 2 and the secondwire 3 to each other by butt seam welding.

In the step 1, the first wire 2 and the second wire 3 are fixed(mounted) to a butt welder (not shown).

In the step 2, the connection end face 21 on the proximal side of thefirst wire 2 and the connection end face 31 on the distal side of thesecond wire 3 are butted to each other while a specific voltage isapplied thereto by the butt welder. With this operation, a fused layer(welded surface) is formed at the contact portion, whereby the firstwire 2 and the second wire 3 are strongly joined to each other.

In the step 3, a projection at the joining portion (welded portion 14),which is formed by deformation upon butt resistance welding, is removed.A portion, on the proximal side from the welded portion 14, of thesecond wire 3, that is, the distal end portion of the second wire 3 isground, to form the small cross-sectional area portion 32 having adesired shape as shown in FIG. 1, 5, or 6, that is, the smallcross-sectional area portion 32 with its outer diameter graduallyreduced in the direction toward the distal end.

Alternatively, the small cross-sectional area portion 32 having adesired shape (with its outer diameter gradually reduced in thedirection toward the distal end) may be previously prepared by grindingthe distal end portion of the second wire 3, and then welded to thefirst wire 2 by the butt resistance welding process.

FIGS. 3 and 4 are views showing the operational state of the guide wire1 of the present invention during use in the PTCA process.

In FIGS. 3 and 4, reference numeral 40 denotes an aortic arch, 50 is aright coronary artery of a heart, 60 is an ostium of the right coronaryartery 50, and 70 is a target angiostenosis portion. Further, referencenumeral 30 denotes a guiding catheter for certainly guiding the guidewire 1 from an arteria fermoralis into the right coronary artery 50, and20 is a balloon catheter having at its distal end an expandable andcontractible balloon 201 for dilating the target angiostenosis portion70.

As shown in FIG. 3, the guide wire 1 is moved in such a manner that thedistal end thereof projecting from the distal end of the guidingcatheter 30 is inserted in the right coronary artery 50 through theostium 60 of the right coronary artery 50. The guide wire 1 is furtheradvanced, and is stopped when the distal end thereof passes the targetangiostenosis portion 70 in the right coronary artery 50. In this state,an advance path of the balloon catheter 20 is ensured. At this time, thewelded portion 14 of the guide wire 1 is located in the living body,more specifically, in the vicinity of the distal portion of the aorticarch 40.

As shown in FIG. 4, the balloon catheter 20 is inserted around the guidewire 1 from the proximal side of the guide wire 1. The balloon catheter20 is then advanced in such a manner that the distal end thereofprojects from the distal end of the guiding catheter 30, goes aheadalong the guide wire 1, and enters the right coronary artery 50 from theostium 60 of the right coronary artery 50. The balloon catheter 20 isstopped when the balloon 201 reaches a position corresponding to that ofthe target angiostenosis portion 70.

A fluid for inflating the balloon 201 is injected in the ballooncatheter 20 from the proximal side of the balloon catheter 20, toinflate the balloon 201, thereby dilating the target angiostenosisportion 70. As a result, deposits such as cholesterol adhering on thearterial wall of the target angiostenosis portion 70 are physicallycompressed against the arterial wall, to eliminate blocking of bloodflow.

FIG. 7 is a longitudinal sectional view showing a second embodiment ofthe guide wire of the present invention. The second embodiment of theguide wire of the present invention will now be described with referenceto FIG. 7, principally, about differences from the previous embodiment,with the description of the same features omitted.

According to a guide wire 1′ in this embodiment, a first wire 2 has anouter-diameter gradually reducing portion 22 and an outer-diametergradually reducing portion 24 provided on the proximal side from theouter-diameter gradually reducing portion 22. In this way, the firstwire 2 may have outer-diameter gradually reducing portions at aplurality of positions.

In this embodiment, a welded portion 14 has a projection 15 projectingin the outer peripheral direction. The formation of such a projection 15is effective to enlarge a joining area between the first wire 2 and thesecond wire 3, and hence to significantly enhance the joining strength.This is advantageous in more certainly transmitting a torsional torqueor pushing force from the second wire 3 to the first wire 2.

The formation of the projection 15 may make the welded portion 14between the first wire 2 and the second wire 3 easily visible underfluoroscopy. As a result, it is possible to easily, certainly recognizethe advancing state of the guide wire 1′ and a catheter in a bloodvessel or the like by checking the fluoroscopic image, and hence toshorten the operation time and to improve the safety.

As described above, the first wire 2 and the second wire 3 are generallymade from materials having different elastic moduli. Accordingly,because of provision of the projection 15, an operator can easily,certainly, recognize a portion, at which the elastic modulus isrelatively largely changed, of the guide wire 1′. This enhances theoperationality of the guide wire 1′, to shorten the operation time andimprove the safety.

The height of the projection 15, which depends on the outer diameters ofthe first wire 2 and the second wire 3, is not particularly limited, butis preferably in a range of 0.001 to 0.3 mm, more preferably, 0.005 to0.05 mm. If the height of the projection 15 is less than the lowerlimit, it may fail to sufficiently obtain the above-described effectsdepending on the materials of the first wire 2 and the second wire 3. Ifthe height of the projection 15 is more than the upper limit, since theinner diameter of a lumen, in which the guide wire 1 is to be inserted,of a balloon catheter is fixed, the outer diameter of the second wire 3on the proximal side must be thin relative to the height of theprojection 15, with a result that it may become difficult to ensuresufficient physical properties of the second wire 3.

In the configuration shown in FIG. 7, each of one side (upper side inFIG. 7) and the other side (lower side in FIG. 7) of the projection 15is formed into an approximately circular-arc shape in longitudinalcross-section, and the welded portion 14 is located on the maximumouter-diameter portion of the projection 15. This is advantageous inenlarging an area of the welded surface of the welded portion 14,thereby obtaining a higher joining strength (welding strength).

According to the present invention, the shape of the projection 15 andthe position of the welded portion 14 relative to the projection 15 arenot limited to those described above. For example, each of one side andthe other side of the projection 15 may be formed into a non-circular(non-circular arc) such as a trapezoidal or triangular shape inlongitudinal cross-section. The proximal side and the distal side of theprojection 15 may be formed into shapes asymmetric to each other withrespect to the welded surface (connection end face 21, 31) of the weldedportion 14. The axial position of the welded surface of the weldedportion 14 relative to the projection 15 is not necessarily located atthe central portion as shown in FIG. 7 but may be located at a positionoffset to the proximal side (second wire 3 side) or on the distal side(first wire 2 side). With this configuration, it is possible to preventor relieve stress concentration at the welded portion 14, and hence tomore certainly prevent breakage of the welded portion 14 due to stressconcentration at the welded portion 14 when a torsional torque orpushing force is applied from the second wire 3 to the first wire 2.

The guide wire 1′ has a cover layer 7 on the outer surface (outerperipheral surface) side. In this way, the guide wire of the presentinvention may be configured to have a cover layer that covers the wholeor part of the outer surface (outer peripheral surface). Such the coverlayer 7 is formed for satisfying various purposes, one of which is toreduce the friction (sliding friction) of the guide wire 1′ forimproving the sliding performance of the guide wire 1′, therebyenhancing the operationality of the guide wire 1′.

To satisfy the above-described purpose, the cover layer 7 is preferablymade from a material capable of reducing the friction of the guide wire1′. With this configuration, since the friction resistance (slidingresistance) of the guide wire 1′ against the inner wall of a catheterused together with the guide wire 1′ is reduced, the sliding performanceof the guide wire 1′ is improved, to enhance the operationality of theguide wire 1′ in the catheter. Further, since the sliding resistance ofthe guide wire 1′ is reduced, it is possible to more certainly prevent,at the time of movement and/or rotation of the guide wire 1′ in thecatheter, kink (sharp bending) or torsion of the guide wire 1′,particularly, in the vicinity of a welded portion of the guide wire 1′.

Examples of the materials capable of reducing the friction of the guidewire 1′ include polyorefins such as polyethylene and polypropylene,polyvinyl chloride, polyesters (such as PET and PBT), polyamide,polyimide, polyurethane, polystyrene, polycarbonate, silicone resins,fluorocarbon resins (such as PTFE and ETFE), silicone rubbers, variouskinds of elastomers (for example, thermoplastic elastomers such aspolyamide-based elastomer and polyester-based elastomer), and compositematerials thereof. In particular, a fluorocarbon resin or a compositematerial thereof is preferable, and PTFE is more preferable.

According to this embodiment, a hydrophilic material or a hydrophobicmaterial can be also used as another preferred example of the materialcapable of reducing the friction of the guide wire 1′. In particular,the hydrophilic material is preferable.

Examples of the hydrophilic materials include a cellulose based polymer,a polyethylene oxide based polymer, a maleic anhydride based polymer(for example, a maleic anhydride copolymer such asmethylvinylether-maleic anhydride copolymer), an acrylic amide basedpolymer (for example, polyacrylic amide or polyglycidylmethacrylate-dimethyl acrylic amide [PGMA-DMAA] block copolymer),water-soluble nylon, polyvinyl alcohol, and polyvinyl pyrolidone.

In many cases, the hydrophilic material can exhibit a lubricatingperformance in a wet (water-absorbing) state. The use of the cover layer7 made from such a hydrophilic material is effective to reduce thefriction resistance (sliding resistance) of the guide wire 1′ againstthe inner wall of a catheter used together with the guide wire 1′, toimprove the sliding performance of the guide wire 1′, thereby enhancingthe operationality of the guide wire 1′ in the catheter.

The provision of the cover layer 7 is effective to omit or simplify theabove-described step filling member 6. To be more specific, since thecover layer 7 is formed in such a manner as to cover a stepped portionin the vicinity of the welded portion 14, even if the step fillingmember 6 is omitted or simplified, it is possible to sufficientlyprevent degradation of the sliding performance of the guide wire 1′ dueto the presence of the stepped portion.

The cover layer 7 may be formed in such a manner as to the whole or partof the guide wire 1′ in the longitudinal direction; however, the coverlayer 7 is preferably formed in such a manner as to cover the weldedportion 14, that is, formed at a portion including the welded portion14.

The cover layer 7 covers the small cross-sectional area portion 32 andthe projection 15, and has a substantially uniform outer diameter. Theterm “substantially uniform outer diameter” used herein contains anouter diameter smoothly changed within such a range as not to cause anyinconvenience in use of the guide wire.

The thickness (in average) of the cover layer 7 is not particularlylimited but is preferably in a range of about 1 to 20 μm, morepreferably, about 2 to 10 μm. If the thickness of the cover layer 7 isless than the lower limit, the effect obtained by formation of the coverlayer 7 may be not sufficiently achieved and the cover layer 7 may beoften peeled. If the thickness of the cover layer 7 is more than theupper limit, the physical properties of the wire may be obstructed andthe cover layer 7 may be often peeled.

According to the present invention, the outer peripheral surface of theguide wire body (including the first wire 2, the second wire 3, and coil4) may be subjected to a treatment (such as chemical treatment or heattreatment) for improving the adhesion characteristic of the cover layer7, or may be provided with an intermediate layer for improving theadhesion characteristic of the cover layer 7.

The cover layer 7 may have a nearly constant composition or differentcompositions at respective portions. For example, the cover layer 7 mayhave a first region (first cover layer) for covering at least the coil 4and a second region (second cover layer) on the proximal side from thefirst region, wherein the first cover layer and the second cover layerbe made from different materials. Although the first cover layer and thesecond layer may be formed so as to be continuous to each other in thelongitudinal direction as shown in the figure, the proximal end of thefirst cover layer may be separated from the distal end of the secondcover layer, or the first cover layer may be partially overlapped to thesecond cover layer.

FIGS. 8A and 8B are perspective views showing further modifications ofthe small cross-sectional area portion of the second wire of the guidewire of the present invention.

A small cross-sectional area portion 32 of a second wire 3 shown in FIG.8A has an outer diameter, which is kept constant and is equal to that ofa portion on the proximal side from the small cross-sectional areaportion 32. The small cross-sectional area portion 32 has a hollowportion 321 with its inner diameter gradually increased in the directiontoward the distal end. That is to say, the hollow portion 321 is formedinto a conical or truncated conical shape. Since such a hollow portion321 is formed, the cross-sectional area of the small cross-sectionalarea portion 32 is smaller than that of a proximal end portion 23 of afirst wire 2 and is gradually reduced in the direction toward the distalend, with a result that the rigidity (flexural rigidity, torsionalrigidity) of the small cross-sectional area portion 32 is graduallyreduced in the direction toward the distal end. According to the presentinvention, such a small cross-sectional area portion 32 having the shapeshown in FIG. 8A has the same effect as that obtained in each of theprevious embodiments. The small cross-sectional area portion 32, inwhich the cross-sectional area can be gradually reduced without changingthe outer diameter by the presence of the hollow portion 321, hasanother advantage in eliminating the need of provision of the stepfilling member 6 because no stepped portion is formed at a weldedportion 14 between the proximal portion 23 of the first wire 2 and thesmall cross-sectional area portion 32. The hollow portion 321 may beformed into a pyramid or truncated pyramid shape. In this case, thewelding may be performed in a state that part of the proximal endportion 23 of the first wire 2 is inserted in the hollow portion 321 ofthe second wire 3. With this configuration, since the change in rigiditybecomes smoother between both sides of the welded portion 14, it ispossible to further improve the kink resistance.

A small cross-sectional area portion 32 of a second wire 3 shown in FIG.8B has a truncated pyramid shape, more specifically, a truncatedhexagonal pyramid shape, wherein the dimension of the polygonal shape(regular hexagonal shape) in cross-section is gradually reduced in thedirection toward the distal end. As a result, the cross-sectional areaof the small cross-sectional area portion 32 is gradually reduced in thedirection toward the distal end, with a result that the rigidity(flexural rigidity, torsional rigidity) thereof is gradually reduced inthe direction toward the distal end. Such a small cross-sectional areaportion 32 shown in FIG. 8B has the same effect as that obtained in eachof the previous embodiments.

In the above-described embodiments, each of the composing elements ofthe guide wire may be replaced with a composing element having any otherconfiguration exhibiting the similar effect, and may be provided withany other additional element.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. A guide wire comprising: a first wire disposed onthe distal side of said guide wire; and a second wire disposed on theproximal side from said first wire; wherein said first wire and saidsecond wire are joined to each other by welding; and said second wirehas a first portion having an outer diameter gradually reduced in adirection toward a distal end of the second wire, and has a secondportion having an outer diameter gradually increased in the directiontoward the distal end of the second wire, wherein the second portion isdisposed on the distal side from the first portion and extends to thedistal end of the second wire.
 2. The guide wire according to claim 1,wherein the first wire and the second wire are joined to each other at awelded portion having a projection that projects in an outer peripheraldirection of the guide wire.
 3. The guide wire according to claim 2,wherein a part of the projection constitutes the second portion.
 4. Theguide wire according to claim 1, wherein the second wire has a smallcross-sectional area portion from the first portion to the secondportion of the second wire, and the small cross-sectional area portionincludes a hollow portion having an inner diameter gradually increasedin the direction toward the distal end of the second wire so that thecross-sectional area of the small cross-sectional area portion issmaller than the cross-sectional area of a proximal end portion of thefirst wire, and is gradually reduced in the direction toward the distalend of the second wire.
 5. The guide wire according to claim 4, whereinsecond wire is made from a material having an elastic modulus largerthan that of said first wire.
 6. The guide wire according to claim 2,further comprising a cover layer disposed over at least said weldedportion.
 7. The guide wire according to claim 4, wherein said smallcross-sectional area portion has an outer diameter smaller than an outerdiameter of the proximal end portion of said first wire.
 8. The guidewire according to claim 1, wherein said first portion of said secondwire has a length in a range of 0.1 to 1,000 times a length of saidsecond portion.
 9. The guide wire according to claim 1, wherein thefirst wire possesses a proximal end face, and the outer diameter of theentirety of the first wire other than the proximal end face is notgreater than the outer diameter of the proximal end face of the firstwire.
 10. The guide wire according to claim 1, wherein the second wirepossesses a distal end face, and the outer diameter of the entirety ofthe second wire other than the distal end face is not greater than theouter diameter of the distal end face of the second wire.
 11. The guidewire according to claim 4, wherein a longitudinal length of the smallcross-sectional area portion is less than a longitudinal length of thefirst wire.
 12. The guide wire according to claim 2, wherein the firstwire and the second wire abut each other at the welded portion withoutany axial overlap.
 13. The guide wire according to claim 1, wherein thesecond wire has a third portion having a constant outer diameter, saidthird portion being disposed between said first portion and said secondportion of the second wire.
 14. The guide wire according to claim 1,wherein the first wire possesses a proximal end face, aconstant-diameter portion, and a tapered portion having an outerdiameter which decreases toward the distal side of the first wire. 15.The guide wire according to claim 14, wherein the tapered portion of thefirst wire is formed on the distal side of the first wire, and theconstant-diameter portion of the first wire is formed on the proximalside of the first wire, and wherein the constant-diameter portionextends from the proximal end face of the first wire to the taperedportion of the first wire and has a greater outer diameter than that ofthe entirety of the first wire other than at the constant-diameterportion.